Epilepsy is a well-known neurological disease, found in about 3% of the population. Approximately 30% of patients with epilepsy do not respond to currently available therapies. Such unfortunate patients—who number hundreds of thousands of people world-wide—must contend with both uncontrolled seizures and the resulting narrowing of their options in such crucial areas of life as health insurance, employment, and driving.
Retigabine (N-[2-amino-4-(4-fluorobenzylamino)phenyl]carbamic acid, ethyl ester) (U.S. Pat. No. 5,384,330) has been found to be an effective treatment of seizure disorders and has also been found useful in treating pain. Retigabine has been found to be particularly potent in models for the drug-refractory types of epilepsy. Bialer, M. et al., Epilepsy Research 1999, 34, 1-41; Blackburn-Munro and Jensen, Eur. J. Pharmacol. 2003, 460, 109-116; Wickenden, A. D. et al., Expert Opin. Ther. Patents, 2004, 14(4).
“Benign familial neonatal convulsions,” an inherited form of epilepsy, has been associated with mutations in the KCNQ2/3 channels. Biervert, C. et al., Science 1998, 27, 403-06; Singh, N. A., et al., Nat. Genet. 1998, 18, 25-29; Charlier, C. et al., Nat. Genet. 1998, 18, 53-55; Rogawski, Trends in Neurosciences 2000, 23, 393-398. Subsequent investigations have established that one important site of action of retigabine is the KCNQ2/3 channel. Wickenden, A. D. et al., Mol. Pharmacol. 2000, 58,591-600; Main, M. J. et al., Mol. Pharmcol. 2000, 58, 253-62. Retigabine has been shown to increase the conductance of the channels at the resting membrane potential, with a possible mechanism involving binding of the activation gate of the KCNQ 2/3 channel. Wuttke, T. V., et al., Mol. Pharmacol. 2005. Additionally, retigabine has been shown to increase neuronal M currents and to increase the channel open probability of KCNQ 2/3 channels. Delmas, P. and Brown, D. A. Nat. Revs Neurosci., vol. 6, 2005, 850-62; Tatulian, L. and Brown, D. A., J. Physiol., (2003) 549, 57-63.
The seizure type that has been most resistant to therapy is the so-called “complex partial seizure.” Retigabine is active in several seizure models, including, as indicated above, models for drug-refractory epilepsy. Because of retigabine's broad spectrum of activity and its unusual molecular mechanism, there is hope that retigabine will be effective in management of several seizure types, including the complex partial seizure, which have been resistant to treatment. Porter, R. J., Nohria, V., and Rundfeldt, C., Neurotherapeutics, 2007, vol. 4, 149-154.
The recognition of retigabine as a potassium channel opener has inspired a search among compounds with structural features in common with retigabine for other compounds which can affect the opening of, or otherwise modulate, potassium ion channels.